1. Field of the Invention
The present invention generally relates to a development device to develop an electrostatic latent image formed on a latent image carrier and an electrophotographic image forming apparatus, such as a copier, a facsimile machine, a printer, or a multifunction device including at least two of those functions, that includes the same.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices including at least two of those functions and the like, include a latent image carrier on which an electrostatic latent image is formed, a development device to develop the electrostatic latent image with developer, and a transfer unit to transfer the developed image (toner image) onto a sheet of recording media. The electrostatic latent image formed on the latent image carrier is developed with either one-component developer consisting of toner or two-component developer including toner and magnetic carrier.
In development devices using two-component developer, the toner concentration in the developer supplied to a development sleeve, serving as a development member, should be kept constant to maintain a constant image density of resulting images.
So-called unidirectional development devices, in which the developer is circulated unidirectionally within a closed circulation path, typically use separate screws to supply the developer to the development sleeve prior to development of the electrostatic latent image and to collect the developer from the development sleeve after development. Certain other known development devices include a separate agitation unit or container containing the toner and the carrier. In the agitation unit, the developer is agitated so that the toner concentration is adjusted to a desired concentration and the toner is charged, and only then the developer is supplied to the development device.
Screws are typically used as agitation members or developer transport members to transport and agitate the developer in the development devices. Certain known development devices use a toner concentration adjuster to adjust the ratio of toner to carry in a container portion. However, when the screw is used as the developer transport member, the amount of charge (hereinafter “charge amount”) of the developer depends on the distance the developer is transported (hereinafter “transport distance”) because the screw agitates the developer while transporting the developer. Thus, the developer charge amount in not uniform but differs depending on the position in the development device at which the developer is carried on the development sleeve, causing differences in the image density of the formed images.
In view of the foregoing, there is a need for the development device to reduce differences in the charge amount of the developer caused by the differences in the transport distance of the developer and thus provide more uniformly charged developer.